Kohler 7000 24 HP surging when lightly loaded

[N_Jay]

QMy craftsman MTD zero turn with the kohler, 7000 24-horse power surges and backfires when unloaded (blades off)
Low or high throttle.

Any ideas?

 

[Firebrick43]

Dirty Carb? Air leak at a sealing surface(bad gasket)? Plugged air filter? Spark Plug or ignition coil going bad? Back fires also are a common cause of sheared fly wheel keys, which in turn causes timing to be off even more.

 

[Stuart in MN]

Surging at light or no load would point me towards plugged jets in the carburetor.

 

[N_Jay]

Are these carbs worth cleaning, or is it better to replace?

 

[LopezBart]

Are these carbs worth cleaning, or is it better to replace?

I usually just clean the jets w/ copper wire. Of course, check your air filter and other easy stuff before tearing into things....

 

[theoldwizard1]

Surging at light or no load would point me towards plugged jets in the carburetor.

As other have said, surging is almost ALWYAS caused by a lean condition. Typically the low speed/pilot/idle jet (not the main jets).

The dirt got in there from the fuel tank. Time to replace/add a fuel filter !

Are these carbs worth cleaning, or is it better to replace?

Yes, it is worth cleaning, unless you are willing to buy a genuine OEM replacement. Aftermarket carbs are typically less than 50/50 !

 

[The Cobbler]

sounds lean. as mentioned... carb most probable cause . yes, it is worth cleaning thoroughly . not many OEM carbs can't be brought back to normal if properly cleaned

 

[BillK]

Yours might be different but ....... I had the same problem with my snow blower about a year ago. I tried cleaning what I thought was the correct jet in the bottom but it turned out to be another jet that I never knew existed. It is called the "pilot" jet. Take a look at this video and see if your carburetor is the same:

 

[theoldwizard1]

... it turned out to be another jet that I never knew existed. It is called the "pilot" jet.

It is almost ALWAYS the pilot jet !

On some carbs is is difficult to located the pilot jet. On smaller engines you might need a micro-drill set (#60-#80) to clear any blockages. Worse, on some Vee engines (Generac), you have to remove the intake manifold and the carb as an assemble.

Check YouTube. There are several videos and cleaning the carb for that engine.

 

[BillK]

It is almost ALWAYS the pilot jet !

On some carbs is is difficult to located the pilot jet. On smaller engines you might need a micro-drill set (#60-#80) to clear any blockages. Worse, on some Vee engines (Generac), you have to remove the intake manifold and the carb as an assemble.

Check YouTube. There are several videos and cleaning the carb for that engine.

I ended up buying a new jet. It was cheap and the old one was so clogged with hard **** that I was too lazy to mess with it. Even my big ultrasonic cleaner wouldnt touch it.

 

[Stuart in MN]

You need to make sure to not use a wire or drill that's too large, since the jets are made of soft brass they can be wallowed out so the hole is too large. There are specific jet cleaning tools, or a micro drill as mentioned. An individual strand cut off a soft fine wire brush may also work. The jet may be clogged with dirt, or it could just be old gas that's gummed up.

 

[N_Jay]

Gas is fairly fresh.
Filer was fresh and few cuts ago (maybe 6 to 9 hours) but the field id really dusty due to our drought. Pre-filer was a mess, so going to clean/change.
Fuel filter looks good. Runs fine at high load.

If it still does it after cleaning the air filter, I might mix up a small amount of gas with a heavy dose of carb/fuelinjector cleaner and run that throught.

 

[theoldwizard1]

I ended up buying a new jet. It was cheap and the old one was so clogged with hard **** that I was too lazy to mess with it. Even my big ultrasonic cleaner wouldnt touch it.

Which is why I said

On smaller engines you might need a micro-drill set (#60-#80) to clear any blockages.

But, if you can find the proper jet they are cheap !

 

[theoldwizard1]

If it still does it after cleaning the air filter, I might mix up a small amount of gas with a heavy dose of carb/fuelinjector cleaner and run that throught.

A dirty air filter will make it run RICH (and not surge).

I have found that carb/fuel injector cleaner is a waste of money.

 

[N_Jay]

Seems to be related to the dirty air filter.
Changed the filter snf it ran well till I finished up another 3 hour cut.
Blew thr filter clean, and agai good for most of s cut, but came back.

Has anyone done one of the the "pro" air filter conversations?

Seems it would be worthwhile.

 

[nadogail]

IMHO, on many mowers the blade serves as the flywheel for the engine, an engine without a flywheel may not run smoothly.

 

[Firebrick43]

IMHO, on many mowers the blade serves as the flywheel for the engine, an engine without a flywheel may not run smoothly.

Maybe push mowers, but 24hp V twins that have an electric clutch and belt drive blades will run just fine without the blades on. The V twins all have a decent size flywheel.

 

[junkyardwarrior]

surging is a lean condition almost 100% of the time.

Why is it lean? Air leaks, and dirt carburetor are the 2 main causes. The latter is probalby 95% of them that I see.

Why would a lean condition cause it? Look at how the carb works. It supplies air to the engine, and the air is responsible for allowing metered amount of fuel to flow with that air. With no or little load, you're running on both the pilot (idle) and the main circuit, leaning more on the pilot than the main. Once you load it, the throttle blade opens up due to the governor, and now you're mostly on the main circuit. The pilot is generally a, or a series of, tiny orifices-and they plug a lot easier than the main circuit does, which is almost always a MUCH larger orifice. When it's lean (plugged pilot or air leak), with little load on it, the engine will run ok up to a certain speed which is dependent on the carburetor usually, with little air flow needed. As the RPM comes up, the engine needs some more fuel. Carb pilot circuit can't supply that needed fuel so the engine slows (it's lean), then the governor "sees" the RPM drop and opens the throttle blade, which gives it a little more fuel, engine speed rises quickly, throttle blade closes as RPM comes up, then the process repeats over and over and over and over and over and over....LOL...until you either shut it off, or put more load on it such that the throttle blade is opened up all the way with a load against it.

Clean the carb. While you have it off, look closely at the intake manfold for cracks where the intake is bolted to the head.

 

[theoldwizard1]

surging is a lean condition almost 100% of the time.

Why is it lean? Air leaks, and dirt carburetor are the 2 main causes. The latter is probalby 95% of them that I see.

On Honda and Honda clone single cylinder engines it is almost always the idle/pilot jet. It can be removed be removed, cleaned and replaced in under 10 minutes without removing the carb !

 

[N_Jay]

I get what you are saying, but it does it towards the end if cutting when the filter is getting dirty, and it doesn't do it at the beginning, or right after cleaning the air filter.

Wonder if it is just a little lag or stiffness in the governor.

At the end of the season it is going to get a good cleaning and service.

Still thinking about the filter conversation. A filter that changes flow noticeably in a single 3 hour run seems under sized.

Also like the idea of pulling cooler air.

 

[bob smith1]

I get what you are saying, but it does it towards the end if cutting when the filter is getting dirty, and it doesn't do it at the beginning, or right after cleaning the air filter.

Wonder if it is just a little lag or stiffness in the governor.

At the end of the season it is going to get a good cleaning and service.

Still thinking about the filter conversation. A filter that changes flow noticeably in a single 3 hour run seems under sized.

Also like the idea of pulling cooler air.

Still playing with this? The governor is NOT your issue, its a result. We call it "hunting". 99% is from a carb or otherwise air/fuel issue.

Before you do anything, first take control of the actual air butterfly on the carb when it's doing it. That means put your hand on it and stabilize it. The engine will now stop surging, but will show you the real behavior. Does the engine act like it will just die? Or does it act like the choke is on? Any black smoke?

Usually its a lean condition. Another very simple test is when doing it, add just a little choke, usually up to 1/2, never full. If you find a spot where it runs right, smooth, etc, you have confirmed a plugged jet.

Another common issue is leaking needle/seat. Again, just cleaning fixes this. You MUST have a filter just before the carb. I totally ignore factory filters if just a screen in the tank or something.

 

[finn]

Listen to those that have been through this many, many times.

 

[N_Jay]

Not trying to ignore you guys, just trying to make it all make sense.
It does have a proper fuel filter.
I haven't pulled the covers off to get to the governor.
I am guessing that what ever the issue is, it is very slight or just starting, since all is good under (near) perfect conditions (clean air filter.)
Since the air filter assembly seems to be part of the engine cover it might be hard to replicate with the cover off.

 

[bob smith1]

You didn't read a word I wrote.

 

[N_Jay]

You didn't read a word I wrote.

Or you didn't read what I wrote.

I don't think i can get a hand/finger on the throttle with the airfilter assembly attached.
Being as it doesn't surge or hunt with a clean filter, i am guessing that it would not with the filter removed.


All the suggestions will be taken into account when I seevice it at the end of the season.

Reading some about air leaks from plastic intake parts.

Thanks all.

 

[bob smith1]

OK...... I'm just the guy with decades of race engine experience, an OEM engine component manufacturer, you see in magazines, and many years as "the tech" people drug their equipment to AFTER they spent a year trying to save money. I already know a competent small engine guy would find your problem in 5min or less. We do very basic things like shut fuel off, add choke, use an inductive ignition tester, etc, to find it.

You're describing a potential 'fat' condition, yet chasing for air leaks.

One thing I'm wondering is if your choke butterfly is not full open.......... I've seen the simplest of things.

 

[N_Jay]

It is not running poorly enough to worry about yet, just odd that the symptom only shows up with a dirty filter.

Also a little surprised that 3 hrs running takes the filter from "clean enough " to "too dirty".

 

[bob smith1]

It is not running poorly enough to worry about yet, just odd that the symptom only shows up with a dirty filter.

Also a little surprised that 3 hrs running takes the filter from "clean enough " to "too dirty".

There are some STRONG indicators there, and they are being ignored. What is on the air filter that is fouling it, and a mower, with only minor filter fouling, won't run right, that points to a fat condition, as in tuning, as in a 1/4 turn and done......

 

[N_Jay]

There are some STRONG indicators there, and they are being ignored. What is on the air filter that is fouling it, and a mower, with only minor filter fouling, won't run right, that points to a fat condition, as in tuning, as in a 1/4 turn and done......

Just dust.
I little better on the last cut since we had some good rain, but spring was dry.

It blows fairly clean with compressed air.
It is a paper pleated filter with a foam cover.
(Google Kohler 7000 filter)

Engine is running well, just bugging me when I disengage the blades and idle.

 

[bob smith1]

And all you have to do is add some choke to learn something.

 

[N_Jay]

And all you have to do is add some choke to learn something.

I will try that, but the choke is combined with the throttle, and choke on to choke off is a fairly short throw.
I am not sur I can get a "little" choke.

 

[bob smith1]

I will try that, but the choke is combined with the throttle, and choke on to choke off is a fairly short throw.
I am not sur I can get a "little" choke.

That whole arrangement seems suspicious to me.

 

[Metallitubby]

And all you have to do is add some choke to learn something.

This sounds like my love life.

 

[bob smith1]

This sounds like my love life.

They either freak TF out, or say "more daddy"...... More issues arise when you can't remember which one likes what........

 

[N_Jay]

That whole arrangement seems suspicious to me.

Typical residential targeted Chraftsman.